1. Field of the Invention
The present invention relates to a process for manufacturing a semiconductor device, especially a process for manufacturing a semiconductor device including the formation of a layer of an aluminum (Al) alloy layer for wiring.
2. Description of Related Art
In recent years, the dominating technology for forming wires of LSIs is to form a film of Al/Cu or Al/Si/Cu on a titanium nitride (TiN), titanium (Ti) film or a multilayer of TiN and Ti films as a barrier metal and then forming a TiN film on the top thereof which serves as an antireflection film at photolithography.
Where the TiN and Ti films are layered for use as the barrier metals for the Al alloy, the TiN film is typically 500 to 1000 .ANG. thick for obtaining practical characteristics of barrier metals, and the TiN film have the orientation of (111) in most cases.
The TiN film and Ti films as the barrier metal are known to be effective for increasing the life of a device against electromigration (hereinafter referred to as EM). The reason is that the TiN and Ti films allow the Al alloy film to develop in the orientation of (111) and have a preventing effect on interface diffusion of the Al alloy, which is a cause of EM disconnection.
It is known that Cu in the Al alloy film separates as an intermetallic compound in a grain boundary of an aluminum polycrystalline film, passivates the grain boundary, reduces voids in the grain boundary and prevents grain boundary diffusion, and thus have effect of improving resistance to EM.
In the layer structure of the Al alloy film, TiN film and Ti film arranged in this order from the top, it is proposed to form the antireflection film on the top of the layer structure at a temperature of 150.degree. C. or lower thereby to improve the EM resistance (Japanese Unexamined Patent Publication No. Hei 7(1995)-99193).
These Ti film and TiN films as the barrier metal are generally formed by a DC magnetron reactive sputtering method, and the TiN film as the antireflection film is formed by a reactive sputtering method wherein the sputtering is performed using a Ti target in an atmosphere of nitrogen. The Ti film, TiN film, Al alloy film and the TiN film serving as the antireflection film thereon are all formed continuously in a single apparatus and then patterned by usual photolithography and dry etching using a reactive ion etching (RIE) technique.
Here, Ti and TiN are usually sputtered under the following conditions: at a pressure of about 2 to 15 mTorr, at a DC power of about 2 to 8 kW, in a chamber for sputtering at a temperature from room temperature to about 300.degree. C. and in an atmosphere of argon. Al/Cu or Al/Si/Cu is usually sputtered under the following conditions: at a pressure of about 5 to 20 mTorr, at a DC power of about 5 to 15 kW, in the chamber for sputtering at a temperature from about 100 to 250.degree. C. and in an atmosphere of argon.
The EM resistance is known to be more excellent as the Al alloy is more highly oriented in a (111) orientation. In order to produce an Al alloy film highly oriented in (111), it is necessary to consider the orientation of a layer (i.e., the barrier metal) under the Al alloy film. As described above, the layer under the Al alloy film is a Ti film or a TiN film in most cases currently. From comparison of Ti and TiN films, it has been found that an Al alloy film more highly oriented in (111) is obtained by placing a Ti film having a (002) orientation immediately under the Al alloy film because of lattice constant. Actually, it has been found that the EM resistance is more improved by placing the Ti film than by placing the TiN film, as an underlayer of the Al alloy film.
However, in the viewpoint of patterning, it has been found that, in the case where the Ti film is used as the layer under the Al/Cu or Al/Si/Cu film, which is typically used as the Al alloy film, fine holes (of about 0.2 .mu.m diameter) appear on sidewalls of wires of the Al alloy during making the Al alloy film into wires, more particularly, during the dry etching using the RIE technique.
In other words, the Al alloy wires are usually formed through the photolithography and the dry etching using the RIE technique. In the case where the Ti film is used immediately under the Al alloy to which Cu is added such as Al/Cu, fine holes (of about 0.2 .mu.m diameter) are open on the sidewalls of the wires after the dry etching (these holes are referred to as side-holes hereinafter). As a result, the reliability of the wires declines.
In order to prevent the generation of the side-holes, a selectivity of a resist at the etching for forming the wires of the Al alloy can be lowered for the purpose of positively forming deposits on the sidewalls of the Al alloy film for protection of the sidewalls. However, this method cannot be applicable to devices having large steps, and therefore, is not an essential side-hole prevention.
On the other hand, it has been found that the TiN film immediately under the Al alloy film have effect of preventing the generation of side-holes. In this case, on the other hand, the EM resistance declines.